I'm not familiar with Rotel products, but I'd suspect that they are a solid product. I would probably look to upgrade the speakers, but really think your problem may be more related to subwoofer integration than any specific component. I "cheat" and have a receiver with Audyssey built in that does a great job of calibration.
Your speakers are spec'd such that they should easily have enough range to blend with a subwoofer without leaving a "hole" in the sound. I wouldn't expect a new amp or pre-amp to correct this.
You could consider going to a receiver with Audyssey, but I don't know how much of a step down that might be from your seperates.
How much time have you spent integrating the subwoofer?
Your speakers are spec'd such that they should easily have enough range to blend with a subwoofer without leaving a "hole" in the sound. I wouldn't expect a new amp or pre-amp to correct this.
You could consider going to a receiver with Audyssey, but I don't know how much of a step down that might be from your seperates.
How much time have you spent integrating the subwoofer?